Palatability is a basis on which the purity of a water supply is judged. A foreign taste and/or odor suggests contamination and that the water may not be safe. However, not all impurities cause such noticeable characteristics. Nitrates, for example, are undetectable by the senses, yet they may be physiologically harmful. In normal quantities, nitrates become toxic under conditions in which they are reduced to nitrites. In humans, consumed nitrates may be reduced to nitrites in the gastrointestinal tract. These nitrites react directly with hemoglobin to produce methemoglobin, which impairs oxygen transport.
Because water is essential to life itself, it has been subjected to treatment by a wide variety of techniques and procedures in an effort to remove impurities which render the water harmful or distasteful. Much effort has been directed toward removing taste and odor causing compounds. U.S. Pat. No. 3,650,949, for example, discloses a method for removing cyanides from water by using copper salts and oxygen. Hydrogen sulfide has been removed from water with copper oxide by Hronas et al. (U.S. Pat No. 3,276,186). Many of these procedures involve the use of activated carbon at some stage of the treatment. Kratz in his patent for "Process of Purifying Water with Activated Carbon" (U.S. Pat. No. 3,017,347), for example, oxidized heavy metal compounds present in water and then passed the treated water through a deep bed of activated carbon. The oxidized heavy metal compounds were adsorbed in the upper portion of the bed while taste and odor causing compounds were adsorbed in the lower portion of the bed.
A more complicated procedure for purifying water was claimed by Bowers in U.S. Pat. No. 3,444,079 for "Method and Apparatus for Demineralizing Water". Bowers first passed water containing organic foulants through a cation exchanger, and then through a bed of activated carbon and then through an anionic exchanger to remove foulants. Gustafson's procedure described in U.S. Pat. No. 3,408,289 for "Method for Waste Water Renovation" is even more complex. Gustafson treated sewage plant effluent by softening, flocculation, filtration, demineralization with a cation exchanger and then passing the pretreated water through activated carbon to remove undesirable organic materials.
Until now, however, an economic and efficient method for selectively removing potentially dangerous nitrates from water has not been available. With concern about the effect of nitrites upon the health and well-being of humans growing, it has become more important than ever to find a relatively simple yet effective means for removing the potential source of nitrites (i.e. nitrates) from water intended for human consumption.